1. Field of the Invention
The present invention relates to a switching circuit and a digital power amplifier, and more specifically, relates to a switching circuit and a digital power amplifier, in which a switching element having a small withstand voltage is employed for switching, so that high power can be supplied to a load.
2. Description of the Related Art
Recently, digitalization of amplifiers which amplify power is making quick progress. Particularly, in the audio amplifiers, digitalization is remarkably adopted in full scale. As equipment equipped with the digital power amplifier (a so-called switching amplifier), there can be mentioned DVD players, minicomponents, television sets, personal computers and portable telephones. This corresponds to the demand for miniaturizing audio amplifiers and achieving low power consumption, which arises as the equipment has high function.
In the switching amplifier, for example, two sets of series circuits consisting of two switching elements are connected between a pair of high and low power supply lines, and a load (speaker) and a low-pass filter are connected between nodes between the switching elements in the respective sets, so that the switching elements are on-off controlled according to a digital signal obtained by converting an acoustic signal, and the acoustic signal returned to an analog signal again by the low-pass filter is supplied to the load.
In audio amplifiers of the analog amplifier, amplifiers having the output power of 1 kW or higher exist at present. On the other hand, in the audio amplifiers employing the digital power amplifier (switching amplifier), the output power thereof is generally from 200 to 300 W.
It is desired that the switching amplifier have high output as high as being capable of realizing an analog amplifier, taking into consideration that the switching amplifier is replaced for an analog amplifier.
However, the conventional switching amplifier has a switching element as an essential component, and the withstand voltage in the switching element restricts the output power, and hence the upper limit of the output power has been from 200 to 300 W.
Therefore, there is a demand for a switching circuit and a digital power amplifier capable of supplying much power to the load, as compared with the conventional circuit.